I think your example is flawed. I'm not sure if it's flamebait as modded above, but let me take a stab at it.
I believe that a better way of putting the parent's arguments would be - moving data over TCP is public domain. I believe we can reason from something being in public domain that it is no longer obvious. Because moving data is no longer "not-obvious", moving a specific type of data is no longer "not-obvious". Things that are obvious are not patentable. Thus, moving a specific type of data is not patentable.
This does not prevent any of the other parts of the process from being patentable. For example: under his suggestion, transmitting VOIP data across the internet is not patentable. But encoding the voice into data still is. And presenting the data on the other side of the connection (as voice, or text, braille, etc) is still patentable.
To extend this: if you created a method by which to encode and transmit a person across TCP/IP as data, it's not patentable. But the process of encoding the person -into- data is. And the process of decoding the person back into a person (or saving to your desktop or whatever) is still patentable. Furthermore, if you invented a way to transmit something other than data across the internet (say, a stab in the face, or gravity), that would still be patentable. So long as it's not data.
It's difficult to put this into your example, but to really stretch your analogy I believe the best way of putting it would be that since using an alphabet to communicate is public domain, languages (different systems that use alphabets to communicate) are not patentable. Books, however, are a display medium, and would still be patentable.